Resin encapsulated lamp assembly



May 30, 1967. E. M. PARKER E 3,322,992

RESIN ENCAPSULATED LAMP ASSEMBLY Filed Feb. 5, 1964 I NVENTORS @MQESW EWIIM pecfia ATTORNEY ing surface, with a second medium United States Patent 3,322,992 I RESIN ENCAPSULATED LAMP ASSEMBLY Edward M. Parker, New Canaan, and Robert E. Ginter,

Milford, Conn., assignors to Penn Keystone Corporation, Ansonia, Conn., a corporation of Pennsylvania Filed Feb. 5, 1964, Ser. No. 342,628 6 Claims. (Cl. 313-111) nate signs and symbols, for pilot and signal lighting, and the like. One of the major drawbacks, particularly in this 7 age of miniaturization, is the hardware necessary to securely mount such. miniature. lamps. Quite often, the hardwareis bulkier than thelamp itself. This is particularly true since the development of the baseless'lamp whose only-external metal elements are the leads providing for electrical connections. Also, lamp. housings are often required, especially where filters andlenses are to be used.

Another factor sometimes causing difficulty is the high operating temperature of miniature lamps, as their radiation surfaces are very small. This problem is particularly accentuated in space vehicles traveling through rarified air having a low thermal conductivity. Another problem encountered with signal lighting is the difficulty of preventing stray lighting which is sometimes. quite undesirable and may be confusing in critical situations. While known means may be used to eliminate stray lighting, such means are quite often heavy or unnecessarily bulky and thus quite unsatisfactory where weight and space are factors to be considered. I 7

Accordingly, it is an object of this invention to provide a lamp assembly which has substantially improved physical properties and which is small and lightweight as compared with known assemblies.

Another object of the invention is to provide a method of manufacturing an improved lamp assembly.

Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.

Generally speaking, the lamp assembly of the instant invention encapsulates. a baseless bulb within a medium so that the bulb is rigidly secured. The fine lead wires connected to the filament through the glass bulb are attached to sturdier terminals or buses, the joints being within the encapsulating material. To prevent stray light and provide maximum useful illumination, all but the irradiating surface of the capsule are coated with a reflective material. To further prevent the escape of stray light and to maximize the heat radiating qualities of the capsule, the capsule is also coated, on all but the irradiathaving improved radiation' qualities,

The encapsulated light assembly to be hereafter described in greater detail, has many advantages, thereby making it adaptable to a variety of "applications. Firstly,

an encapsulated lamp assembly is capable of operating in almost any medium or environment. It is operable in any gas or fluid and is not subject to attack by cor- 'rosive orotherwise, harmful liquids and gases such as salt spray, noxious chemical fumes, fungus and the like. The encapsulation of a lamp not only provides for an assembly of compact size, but also substantially eliminates relative motion between the lamp andi-tsmounting. This is, particularly true in the embodiment utilizinga baseless bulb whichis otherwise diflicult to mount. The

encapsulation also eliminates the hardware normally required for the mounting of both base type and baseless bulbs. As mentioned previously, encapsulation of the lamp results in an increase in the area of the radiating surface, thereby improving the rate of heat transfer or rate of dissipation of the heat. As is well known, high operating temperatures normally decrease the life of a lamp and improved rates of heat transfer will lower the operating temperature within the bulb.'On the other hand, the encapsulation of the bulb within the encapsulating material insulates the surface of the bulb from sudden temperature changes. This increased resistance to thermal shock can also have a substantial beneficial effect on the life of the unit.

The unitary construction of the encapsulated lamp also results in a reduction of weight of the entire assembly by the elimination of many of the hardware elements which would otherwise be required for mounting a lamp.

Again, in connection With unbased bulbs, the encapsulation protects the lead wires and permits utilization of heavier bus material. Joints between the light filament leads and the heavier bus will also be protected against relative movement and destructive environments.

The lamp assembly to be hereafter described also permits utilization of a bulb of lower intensity to provide a desired amount of illumination through control of the emitted light, By eliminating stray light and directing it through a single irradiating surface, higher efficiency of I the light generated results. Through selection and control of the encapsulating material, the uniformity of intensity as well as the intensity of the light irradiated through the irradiating surface may also be controlled. Thus, for a particular application requiring a specified number of lumens of light, a smaller bulb may be used. This effects a reduction in heat generated and a saving in space. Furthermore, the color or wave length of light may also be easily controlled for various applications.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the article possessing the features, properties, and the relation of elements, which are exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.

d For a fuller understanding of the invention, reference is had to the following description taken in connection with the. accompanying drawing, in which:

FIG. 1 is a sectional view taken through the longitudinal axis of a lamp assembly constructed inaccordance with a preferred embodiment of the invention;

)FIG. 2 is an end elevational view of the lamp assembly of FIG. 1'; and V FIG. 3 is a'view similar to FIG. 1, partly in section, showing an alternate construction of a lamp assembly.

Referring now to the basic lamp assembly shown in FIGS. 1 and 2, a baseless bulb or'lamp 11 having a filament 12 is normally provided with leads 13 which extend through the glass bulb or lamp. A bus 14 is provided for each of leads 13 with each lead and its associated bus being electrically connected in any suitable manner such as by welding or soldering. Completely surrounding lamp 11 and leads 13, including the joints between the leads and the bus, is an encapsulating material 15 which is transparent or translucent. The material will be hereafter 7 face. All other surfaces of the capsule are coated with a reflective material 17 which will reflect all light attempting to pass through a coated surface back into the capsule, thereby emitting all light through planar face16. The reflective material is coated with a radiating material 18 which is preferably black. By utilization of a black radiating material, the well-known heat transfer principle of the black box will be utilized to maximize the rate of heat transfer from the assembly.

Mounting of the assembly may be readily accomplished utilizing a variety of known fastening devices selected for the particular application. The mounting hardware selected will preferably be of the type which permits the hardware to be cast as an integral part of the lamp assembly. In this manner, relative motion between the mounting hardware and the lamp assembly is eliminated thereby reducing failures from shock and vibration so often encountered using known mounting techniques.

If filters or lenses are to be used in conjunction with the lamp assembly, they can be molded as an integral part thereof to form the assembly shown in FIG. 3. In FIG. 3, a filter 19 abuts the planar face 16 of the encapsulating material 15. The reflective and radiating material will preferably overlie the edge of filter 19 to prevent stray light and maximize heat transfer. The emitted light will thereupon take on the wavelength or properties of the filter. On the other hand, if a converging or diverging lens is molded in the assembly in place of the filter, then the emitted light will be affected by its passage through the lens. Obviously, combinations of filters or lenses can be utilized as desired for any particular application.

The basic assembly preferably utilizes a lamp of the unbased type. While miniature lamps are normally used, there is no limitation on the size. When manufacturing an assembly utilizing an unbased lamp, which is usually provided with fine leads extending through the glass bulb connected to the filament, bus wires are first soldered or welded to the leads. The bus wire may be in the form of a terminal or it may have any other suitable configuration dependent upon the assembly application. The lamp subassembly, including the bus wires, is mounted in a mold suitable for casting.

Before receiving the molding material, the mold is preferably preheated to the curing temperature which is usually in the range of 225 F. The mold is thereafter filled with the molding material. The molding material primarily consists of one of the commercially available clear or water white epoxy or other thermosetting resins. The epoxy resin consists of a mixture, by Weight, of 97% lowviscosity base resin and 3% hardener. A 1% by weight flexibilizing additive may be added to the mixture to reduce internal stress and improve machiuability. At several stages of the compounding of the molding material, the materials are de-gassed to reduce the likelihood of air or gas inclusions in the capsule. Luminescent and color pigments may also be added to the molding material during the compounding thereof in accordance with the desired properties of the final product. The luminescent pigments improve the intensity and uniformity of the emitted light. A mold material containing 3% by weight of daylight luminescent pigment has proven most effective. The mold material is mixed using a dispersator operated at a speed sufliciently slow to prevent frothing and aeration of the material.

After thorough mixing of the resin, the pigments and the hardener, the mold material is poured over the bulb and bus connections into the preheated mold and the material is cured in an oven for a suitable period. A curing cycle of 16 hours at 225 F. has proven quite satisfactory. However, new developments in compounding could substantially reduce this curing time cycle.

Upon removal from the oven, the mold is cooled before the molded assembly is removed from the mold. Cooling at a rate of F. per minute or slower is preferred to prevent undue stresses and possible cracking of the molded material. It should be noted that the curing cycle causes shrinkage of the molded material. Dimensional design must allow for such shrinkage.

After the molded assembly has cooled sufficiently and the assembly has been removed from the mold, a formulation of white epoxy thermosetting paint is sprayed over the external surfaces of the assembly. The irradiating surface may either be protected to prevent it being coated with paint, or the entire assembly may be painted, with the irradiating surface being machined clear at a later time. The epoxy paint is cured at a temperature of approximately F. for about 30 minutes before machining. The white epoxy paint provides internal reflectivity of the light generated by the encapsulated bulb to provide maximum concentration of light within the capsule and permit emission through the uncoated surface only.

All surfaces except the irradiating surface are then sprayed with a formulation of black epoxy thermosetting paint which is also cured for 30 minutes at a temperature of approximately 175 F. The black coating provides additional insurance against the emission of stray light through the coated surfaces and also converts the assembly into a so-called black box for maximum heat transfer away from the filament heat source.

As previously mentioned, the encapsulation of the lamp within the epoxy material which has insulating qualities, also increases the thermal mass of the assembly. By increasing the thermal mass, the thermal time constant of the unit is also increased and thermal shock to the bulb and filament, when subjected to an abrupt change in environmental temperature, will be substantially reduced or minimized. Changes in physical size due to thermal expansion or contraction will also be substantially slowed, thereby reducing the likelihood of critical differential expansion and contraction in the neighborhood of the glass-t0-metal seal around the filament lead wires. Stresses in the thermal transient state will also be reduced with the resultant reduction of possible damage to the glass bulb.

As can be seen, a sealed unit providing maximum illumination can be constructed in a minimum volume. The internal reflectivity further permits utilization of a smaller bulb to develop the required lumens of light for a particular application. By way of example, a test was run on an illuminated panel for manned spacecraft. Utiliz' ing assemblies constructed in accordance with the instant invention as compared with those known in the art, the panel area was reduced by a factor of approximately 2 to l and the depth behind the panel was reduced by a factor of approximately 4 to 1. Substantial weight savings also resulted in comparison with other standard methods. Espeically in the field of orbital and interplanetary vehicles where two ultimate factors of utmost importance are space and weight considerations, the advantages of the instant invention are quite apparent.

In certain applications, it may be desirable to utilize a light-rectifying device such as an overlay filter or lens in conjunction with the lamp assembly. Such an element can be bonded to the irradiating surface utilizing a clear bonding material after the basic assembly has been molded and cured. It 'is preferable to continue the exterior coatings over the edges of the filter or lens to assure that the completed assembly will have properties consistent with those of the basic light assembly.

It should also be noted that there is no limitation on the number of lamps that can be molded into a single assembly. If it is desired to have a plurality of colors within a single assembly, then a colored coating would be ap plied to the bulbs before being molded into the encapsulating material. Obviously, the basic assembly or variations thereof have an unlimited number of uses. Because the encapsulating material is readily cast or molded and easily machined, the assemblies can be adapted to a variety of applications, shapes, sizes and mounting methods.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efliciency attained and, since certain changes may be made in carrying out the above method and in the article set forth without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims A are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

What is claimed is:

1. A lamp assembly having at least one baseless bulb having a filament encapsulated therein and a plurality of leads which extend from the filament and out through the bulb, a bus electrically connected to each of said leads, the improvement characterized in that a cured thermosetting resin translucent capsule completely encases said bulb, said leads and a porton of said buses, said capsule having a plurality of external surfaces, a cured thermosetting resin reflecting coating covering and adhering to all but a portion of said external surfaces of said capsule, and a cured thermosetting resin radiating coating covering and adhering to said reflecting coating, whereby said uncovered surface portion of said capsule permits light to be emitted from the bulb.

2. A lamp assembly according to claim 1, characterized in that the uncovered surface portion of said capsule is substantially planar.

3. A lamp assembly according to claim 2, characterized in that the capsule is substantially cylindrical and in that the substantially planar uncovered surface portion is one end surface of the cylinder.

4. A lamp assembly according to claim 1, characterized in that the thermosetting resins of said capsule, said reflecting coating and said radiating coating, are an epoxy thermosetting resin.

5. A lamp assembly according to claim 1, in which a filter is secured to the uncovered portion of said capsule.

6. A lamp assembly according to claim 1, in which a lens is secured to the uncovered portion of said capsule.

References Cited UNITED STATES PATENTS 2,023,558 12/1935 Tallman 313-113 2,096,360 10/1937 Heller Q 313-315 X 2,419,432 4/1947 Wright 313-113 2,943,222 6/1960 Colson 313 -198 3,087,982 4/1963 Hayes 313-3 12 X 3,218,500 11/1965 Wright et a1 3133 12 J. LAWRENCE, Primary Examiner. P. C. DEMEO, Assistant Examiner. 

1. A LAMP ASSEMBLY HAVING AT LEAST ONE BASELESS BULB HAVING A FILAMENT ENCAPSULATED THEREIN AND A PLURALITY OF LEADS WHICH EXTEND FROM THE FILAMENT AND OUT THROUGH THE BULB, A BUS ELECTRICALLY CONNECTED TO EACH OF SAID LEADS, THE IMPROVEMENT CHARACTERIZED IN THAT A CURED THERMOSETTING RESIN TRANSCLUCENT CAPSULE COMPLETELY ENCASES SAID BULB, SAID LEADS AND A PORTION OF SAID BUSES, SAID CAPSULE HAVING A PLURALITY OF EXTERNAL SURFACES, A CURED THERMO- 